Gearless drive for cement mill

ABSTRACT

A gearless drive for the drum of a cement mill or the like wherein the pole wheel, i.e. the rotor of a low-speed electric motor surrounds the drum and is connected to it by a circumferential array of uniformly spaced studs which project radially from the drum and are received in a similar array of uniformly spaced recesses located in the pole wheel structure. Elastic members located between each side of each stud and the corresponding end of the recess provide a resilient drive for the drum by the pole wheel, and expansions and contractions of the drum due to changes in temperature are accommodated by sliding movement of the studs in their recesses thus preventing deformations of the drum caused by heat from exerting any forces upon the pole wheel.

United States Patent [54] GEARLESS DRIVE FOR CEMENT MILL 3 Claims, 3Drawing Figs.

52 US. Cl 310/218,

I 310/267 [51] Int. Cl t HOZk 1/28 [50] Field ol'Search 310/261.

[56] References Cited FOREIGN PATENTS 1,078,680 3/1960 Germany 310/2181,196,779 7/1965 Germany 310/218 Primary Examiner-Milton O. l-lirshfieldAssistant Examiner-B. A. Reynolds Attorney-Pierce, Scheffler & ParkerABSTRACT: A gearless drive for the drum of a cement mill or the likewherein the pole wheel, i.e. the rotor of a low-speed electric motorsurrounds the drum and is connected to it by a circumferential array ofuniformly spaced studs which project radially from the drum and arereceived in a similar array of uniformly spaced recesses located in thepole wheel structure. Elastic members located between each side of eachstud and the corresponding end of the recess provide a resilient drivefor the drum by the pole wheel, and expansions and contractions of thedrum due to changes in temperature are accommodated by sliding movementof the studs in their recesses thus preventing deformations of the drumcaused by heat from exerting any forces upon the pole wheel.

PVATENTEU m 2mm SHEET 1 [IF 2 gen Meyer PM 4 x Pm GEARLESS DRIVE FORCEMENT MILL This invention relates to an improved gearless drive forcement mills and the like, and more particularly to a gearless drive ofthe type wherein the pole wheel rotor of a low-speed electric motorsurrounds and is: secured to the mill drum and is surrounded by thestator element of the motor.

In the past, it has been the practice to drive the drum of a cement millover reduction gearing by relatively high-speed electric motors. Forthis purpose, a ring gear has been secured around the drum and the ringgear has been meshed with one or several drive pinions distributedcircumferentially around the ring gear. This ensures a very slow speedof rotation for the drum, which is necessary for operation of a cementmill.

With increasing size of the mill drums, and correspondingly higherdriving torques needed, it was found that a directly driven drumrepresents a much better solution, since the transmission gearingtogether with its lubrication plant requires considerable space and alsoresults in an additional power input requirement, particularly duringstarts and acceleration of the drum with its contents. Moreover, thetransmission gearing requires costly attendance and maintenance.

It has already been suggested to use the drum as a shaft for the polewheel, that is the rotor element of themotor, and to locate the statoraround the mill. However, during operations of the mill, the drum canincrease to a temperature which is 100 C. hotter than the pole wheel.Moreover, after the mill has been shut down, temperature differences ofabout 50 C. may appear on the circumference of the drum. Consequently,deformations appear which are transmitted to the pole wheel and whichwould reach to a considerable overall strain in cases of drums whichhave a-diarneter of several meters.

In order to eliminate this disadvantage of the direct drive, it is knownto secure the pole wheel of the motor not directly to the drum butrather to interconnect it with the drum by way of an elastic coupling inthe form of a circular array of elastic, rod-shaped elements which aredesigned as a spring pack, the outer ends of the rod-shaped elementsbeing secured to the pole wheel and the inner ends to the mill drum. Inthe spoked wheellike connection between polewheel and drum, which formsa statically undefined system, .the individual springs cannot adaptthemselves, however, to thexirregular load caused by the above-mentionedtemperature differences, and consequently the life of such anarrangement is very limited.

The object of the present invention is to provide an improved electricmotor powered gearless drive for the drum of a cement mill, the motorbeing of the low-speed type and whose pole wheel i.e. rotor and statorelements surround the drum, and which includes an elastic connectionbetween the pole wheel and drum which is very simple, rugged andreliable from a structural point of view, but which does not transmit tothe pole wheel rim any deformations of the drum caused by thermalexpansions and contractions in radial and tangential directions. This isattained, in accordance with the invention by designing theinterconnections between the pole wheel and drum as a circumferentiallyextending array of studs which project radially'frorn the drum andengage in correspondingly located recesses in the rim of the pole wheel,thestuds being elastically supported in the recewes by means of elasticelements located between the opposite ends of the recesses, as measuredin a circumferential direction, and the opposite sides of the studs.

A representative embodiment of the invention will now be described indetail and is illustrated in. the accompanying drawings wherein:

FIG. 1 shows a part of the drive in axial section;

FIG. 2 is a fragmentary view'showing a portion of the rim of the polewheel as viewed in the axial direction of the drum; and

FIG. 3 is a view in perspective of one of the elastic elementsinterposed between the pole wheel and the mill drum.

With reference now to the drawings, a fragment of the drum of a cementmill is'indicated at 1, and'thisisdrivendirectly by means of alow-speed, alternating current electric motor, the stator of the motorbeing indicated at 2, and the rotor or pole wheel being indicated at 3.A ring 4 encircles the drum and is welded thereto, and to this ring issecured arim portion 5 by means of a plurality of circumferentiallyspaced bolts 4a. Projecting radially outward from rim 5 is acircumferential array of uniformly spaced studs or projections 6 whichare received respectively in a corresponding circumferential array ofuniformly spaced recesses 7 that open inwardly from the inner portion 8of the pole wheel sn-ucture 3, As can be seen from FIG. 2, anelastic-type drive assembly is located between-each side of theprojection 6 and the corresponding end of the recess 7. Each elasticdrive assembly includes a pair of like, beam-type elastic members 9,shown in detail in FIG. 3, arranged front-to-front, with their outer endportions 9a in contact with each other and with their intermediateportions 9b spaced slightly apart to establish the desired elastic orspring action in a circumferential direction when the pole wheel drivesthe drum. Positive stop projections are located at the opposite ends ofeach recess 7 and these have a rounded end which engage with a flatmiddle portion of the adjacent elastic member 9. A plate 11 made of anabrasion-resistant material such as bronze secured to each side of theprojection 6 has rounded end which engages a flat middle portion of theadjacent elastic member 9. Thus, the contact members 10 and 11 arelocated at about the same radial distance from the center of the drumand exert their forces against the middle portions 9b of the elasticmembers 9. The plates 11 enhance the ability of the studs to slideradially with respect to the elastic members 9, i.e. radially withrespect to the pole wheel 3 as the mill drum expands or contracts. Inorder to exclude dust from reaching the interior of the recesses 7 andperhaps jamming the elastic members 9 to prevent them from functioningproperly, each recess may be walled off by means of side plates 12 whichare shown in FIG. 1.

The elastic members 9 of each pair are prestresscd by means of asuitable clamping arrangement in the direction towards one another,andthe dimensions of the members 9 between their center parts 9b are sochosen that in case of a short circuit of the machine, the center parts9b actually touch each other and thus transmit the short circuit torquedirectly. Due to the special form, a unifonn distribution of the load isachieved at the same time.

The improved interconnection between the drum and pole wheel of theelectric motor, in accordance with the invention is thus extremelysimple, space saving and requires no attention. The individual elasticelements can adapt themselves readily to the unequal forces which arecaused by temperature differences on the drum shell, and the thermalexpansions in a radial direction are absorbed by the.sliding movement ofthe studs in the recesses, so that transmission of any deformation ofthe drum to the pole wheel of the motor is positively prevented.

I claim:

1. A gearless drive for the drum of a cement mill or the like comprisinga low-speedelectric motor surrounding said drum, said motor beingconstituted by an outer stationary stator and an inner rotor of the polewheel type, and means interconnecting said drum and rotor which includea circumferential array of uniformly spaced studs structurally unitedwith said drum and which project in a radially outward directiontherefrom, a corresponding array of uniformly spaced recesses located onsaid rotor in which said-studs are received, and elastic means locatedbetween each side of each stud and the corresponding end of the recessfor providing a driving connection between said rotor and drum, saidelastic means at each side of each stud beingconstituted by a pair oflike elastic members arranged in front-to-front relation, the outer endportions of said elastic members being in contact with each other andthe intermediate portions thereof being spaced slightly from each otherto establish a driving elasticity in the circumferential direction, andsaid studs being free to shift radially in said as defined in claim 1and which further includes means providing a surface ofabrasion-resistant material such as bronze between each side of eachstud and the adjacent elastic member.

1. A gearless drive for the drum of a cement mill or the like comprisinga low-speed electric motor surrounding said drum, said motor beingconstituted by an outer stationary stator and an inner rotor of the polewheel type, and means interconnecting said drum and rotor which includea circumferential array of uniformly spaced studs structurally unitedwith said drum and which project in a radially outward directiontherefrom, a corresponding array of uniformly spaced recesses located onsaid rotor in which said studs are received, and elastic means locatedbetween each side of each stud and the corresponding end of the recessfor providing a driving connection between said rotor and drum, saidelastic means at each side of each stud being constituted by a pair oflike elastic members arranged in frontto-front relation, the outer endportions of said elastic members being in contact with each other andthe intermediate portions thereof being spaced slightly from each otherto establish a driving elasticity in the circumferential direction, andsaid studs being free to shift radially in said recesses to accommodatethermally produced expansions and contractions of said drum.
 2. Agearless drive for the drum of a cement mill or the like as defined inclaim 1 wherein said elastic members of each pair are provided withmeans for prestressing the same.
 3. A gearless drive for the drum of acement mill or the like as defined in claim 1 and which further includesmeans providing a surface of abrasion-resistant material such as bronzebetween each side of each stud and the adjacent elastic member.